Think you've kissed the Blarney Stone? Then think again...

Well, Sir Winston Churchill kissed the Blarney Stone, and it worked for him, didn't it? He was, after all, one of the world's greatest orators. It shows, doesn't it, that there's substance to the legend that it bestows eloquence?

Except that, if a new book on Cork's Blarney Castle is correct, Sir Winston may have kissed the wrong stone and must therefore owe his rhetorical skills to other factors.

Right castle, wrong stone, is the verdict of an archaeologist and architectural historian, Mark Samuel, who has researched the castle and the stone which has for centuries been said to bestow those whose lips touch it with the power to persuade, flatter, coax and soft-soap.

He believes the stone with the allegedly magical powers was quietly redesignated some time in the 19th century. The reason was health and safety, since the people who then owned the castle wanted to attract more tourists but also wanted to make sure none of them plummeted from the high-placed, dangerous rock to their deaths.

Today, hundreds of thousands are making the trek each year, coming into contact with the stone in complete safety. But, if Mr Samuel is right, they have all been under a giant delusion, puckering up at the wrong rock.

"It was all part of the phenomenon of reinventing the castle that happened in the past 200 years as a romantic spot," according to Mr Samuel. "There are quite good grounds now for saying that there is a Blarney Stone in the castle somewhere, but not the one that people are kissing. That has only been identified as the Blarney Stone since about 1870."

The suspicion is that visitors were redirected at that time to a different stone which was more accessible and less hazardous to reach. Today, a bit of leaning is involved but no danger.

This theory is dismissed by the castle's owner, Charles Colthurst, who – perhaps unsurprisingly – describes it as "a load of Blarney". He added: "I would like to assure the millions of people who have kissed the stone in the past that this is the exact location and has been since as far back as all historical records show. The only stone that was ever kissed in Blarney is the stone they kiss today."

Queen Elizabeth I gave the word its pejorative sense, so they say, when she became exasperated with a local chieftain who came up with ever more ingenious excuses for not fulfilling a pledge to hand the castle over to her.

"Odds bodkins!" she is said to have exclaimed. "Blarney, Blarney, I will hear no more of this Blarney!" This sense of the word is also evident in an 18th-century jibe that kissing the stone imparted "the privilege of telling lies for seven years".

Today, the word is in widespread use, most obviously as the title of Irish pubs: there are Blarney Stone bars from Seattle to Amsterdam, from Scunthorpe to Melbourne and from Finsbury Park to Toledo, Ohio.

The questioning of the stone's authenticity is unlikely to dim its popularity for, in addition to its gift of the gab, it has many more myths to offer. It is Jacob's Pillow, some say, brought to Ireland by Jeremiah. It is associated with a saint, Columba, they say, and with Robert the Bruce – in fact it may even be a part of the Stone of Scone. It has also been connected to the Crusades; and, finally, it may be the stone that Moses struck to bring forth water. It seems highly likely that whoever gathered all these myths must themselves have come into close contact with the Blarney Stone.